Altered Ca2+ Responses in Muscles with Combined Mitochondrial and Cytosolic Creatine Kinase Deficiencies

Abstract

We have blocked creatine kinase (CK)-mediated phosphocreatine (PCr) -->/<-- ATP transphosphorylation in skeletal muscle by combining targeted mutations in the genes encoding mitochondrial and cytosolic CK in mice. Contrary to expectation, the PCr level was only marginally affected, but the compound was rendered metabolically inert. Mutant muscles in vivo showed significantly impaired tetanic force output, increased relaxation times, altered mitochondrial volume and location, and conspicuous tubular aggregates of sarcoplasmic reticulum membranes, as seen in myopathies with electrolyte disturbances. In depolarized myotubes cultured in vitro, CK absence influenced both the release and sequestration of Ca2+. Our data point to a direct link between the CK-PCr system and Ca2+-flux regulation during the excitation and relaxation phases of muscle contraction.

Cytoarchitectural and metabolic adaptations in muscles with mitochondrial and cytosolic creatine kinase deficiencies

“…We think that NMR data give a better reflection of the actual metabolite levels than the chemical method, because minor energy metabolite changes can be induced by the freezing procedure. In another report [42] we have provided evidence that the PCr pool does not exchange with ATP and is metabolically completely inert, even under conditions of complete hypoxia. This leaves the question how and when Earlier, we had reported that resting-state glycogen content and the ability to consume this glycogen was about 60% increased in M-CK muscle compared to wild-type [28] mainly due to an increase in fast-type fibers.…”

“…Details on the physiological consequences of CK ablation have been published [13,31,42]. All observations relate to the testing of muscle performance upon artificial electrical stimulation, ex vivo.…”

“…generation of burst activity; [13,28]) in skeletal muscle. If combined with M-CK deficiency, but not singly, ScCKmit deficiency leads to increase in relaxation time [42].…”

Introduction toin vivo31P magnetic resonance spectroscopy of (human) skeletal muscle

“…6(F)), a clear demonstration that the magnitude of exchange had decreased below MRS detection. In these mice PCr was found to be almost metabolically inactive (Steeghs et al 1997;In 't Zandt et al 1999a). This technique has also been applied to human skeletal muscle (for example, see Rees et al 1989).…”

Creatine: a miserable life without it

“…This is facilitated by keeping the local ATP/ ADP ratio high at subcellular sites near cellular ATPases via associated cytosolic MM-CK; this is especially important, for example, in the vicinity of the energetically highly demanding Ca 2+ -ATPase or calcium pump at the sarcoplasmic reticulum (SR), or in conjunction with the sarcolemma Na + /K + -ATPase, where fractions of cytosolic MM-CK are co-localized (Wallimann et al 2011). Supporting such an explanation is the most striking phenotype of the double-CK knockout mouse, which presents with significant difficulty with muscle relaxation (Steeghs et al 1997;Abraham et al 2002), or conversely, by keeping the ADP/ATP ratio high in the vicinity of the mitochondrial ADP/ATP-carrier (ANT) in a tight functional micro-compartment with mitochondrial mtCK (Wallimann et al 2011).…”